Co2 refrigeration system

ABSTRACT

A CO 2  refrigeration system for an ice-playing surface comprises an evaporation stage in which heat is absorbed from an ice-playing surface. CO 2  compressors in a compression stage compress CO 2  refrigerant subcritically and transcritically. A gas cooling stage has a plurality of heat-reclaim units reclaiming heat from the CO 2  refrigerant. A pressure-regulating device is downstream of the gas cooling stage, to control a pressure of the CO 2  refrigerant in the gas cooling stage. A reservoir is downstream of the pressure-regulating device for receiving CO 2  refrigerant in a liquid state. A controller operates the pressure-regulating device to control the pressure of the CO 2  refrigerant in the gas cooling stage as a function of the heat demand of the plurality of heat-reclaim units, the controller causing the pressure of the CO 2  refrigerant to reach a transcritical level as a function of a heat demand of the plurality of heat-reclaim units.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of Ser. No. 14/831,170 filedon Aug. 20, 2015, which is a continuation of U.S. patent applicationSer. No. 13/124,894, which is a national phase entry of PCT/CA09/01536,filed on Oct. 23, 2009, which claims priority on U.S. Patent ApplicationNo. 61/107,689, filed on Oct. 23, 2008, No. 61/166,884, filed on Apr. 6,2009, and No. 61/184,021, filed on Jun. 4, 2009, the entire contents ofeach of which is incorporated by reference herein.

FIELD OF THE APPLICATION

The present application relates to refrigeration systems, and moreparticularly to refrigeration systems using CO₂ refrigerant.

BACKGROUND OF THE ART

Wth the growing concern for global warming, the use ofchlorofluoro-carbons (CFCs) and hydrochlorofluorocarbons (HCFCs) asrefrigerant has been identified as having a negative impact on theenvironment. These chemicals have non-negligible ozone-depletionpotential and/or global-warming potential.

As alternatives to CFCs and HCFCs, ammonia, hydrocarbons and CO₂ areused as refrigerants. Although ammonia and hydrocarbons have negligibleozone-depletion potential and global-warming potential as does CO₂,these refrigerants are highly flammable and therefore represent a riskto local safety. On the other hand, CO₂ is environmentally benign andlocally safe.

SUMMARY OF THE APPLICATION

It is therefore an aim of the present disclosure to provide a CO₂refrigeration system that addresses issues associated with the priorart.

Therefore, in accordance with a first embodiment of the presentapplication, there is provided a CO₂ refrigeration system for anice-playing surface, comprising: a supra-compression portion comprisinga supra-compression stage in which CO₂ refrigerant is supra-compressedand a cooling stage in which the supra-compressed CO₂ refrigerantreleases heat; a condensation reservoir accumulating a portion of theCO₂ refrigerant in a liquid state; pressure-regulating means between thesupra-compression portion and the condensation reservoir to control apressure of the supra-compressed CO₂ refrigerant being directed to thecondensation reservoir; and an evaporation stage receiving the CO₂refrigerant from the condensation reservoir, the evaporation stagehaving a circuit of pipes arranged under the ice-playing surface,whereby the CO₂ refrigerant circulating in the circuit of pipes of theevaporation stage absorbs heat from the ice-playing surface.

Further in accordance with the first embodiment, the system furthercomprises a secondary refrigerant circuit in which circulates asecondary refrigerant, and wherein the supra-compression portioncomprises at least one heat reclaim exchanger related to the secondaryrefrigerant circuit, the at least one heat reclaim exchanger causing thesupra-compressed CO₂ refrigerant to release heat to the secondaryrefrigerant.

Still further in accordance with the first embodiment, the heat reclaimexchanger and the gas cooling stage are in at least one of a parallelarrangement, and a series arrangement.

Still further in accordance with the first embodiment, the systemfurther comprises at least one water tank in the secondary refrigerantcircuit, with the at least one water tank comprising a heat exchanger inwhich circulates the secondary refrigerant to heat water in the watertank.

Still further in accordance with the first embodiment, the secondaryrefrigerant circuit further comprises at least one water tank, with theat least one water tank comprising a heat exchanger in which circulatesthe CO₂ refrigerant to heat water in the water tank.

Still further in accordance with the first embodiment, the secondaryrefrigerant circuit comprises at least one melting heat exchanger in anice dump, the melting heat exchanger receiving secondary refrigerant torelease heat to zamboni residue in the ice dump.

Still further in accordance with the first embodiment, the systemfurther comprises a suction line extending from a top of thecondensation reservoir to an inlet of the supra-compression stage, witha valve in said suction line, such that gaseous CO₂ refrigerant in thecondensation reservoir is directed to the supra-compression stage.

Still further in accordance with the first embodiment, the systemfurther comprises a heat exchanger in said suction line for heatexchange between the gaseous CO₂ refrigerant and CO₂ refrigerant exitingthe cooling stage.

Still further in accordance with the first embodiment, the systemcomprises a pressure-controlling unit in said suction line to control apressure differential between the condensation reservoir and thesupra-compression stage.

Still further in accordance with the first embodiment, the systemfurther comprises an expansion stage between the condensation reservoirand the evaporation stage to vaporize the CO₂ refrigerant fed to thecircuit of pipes.

Still further in accordance with the first embodiment, the systemfurther comprises at least one pump between the condensation reservoirand the evaporation stage to induce a flow of CO₂ refrigerant to theevaporation stage.

Still further in accordance with the first embodiment, thesupra-compression stage compresses the CO₂ refrigerant to atranscritical state.

In accordance with a second embodiment of the present application, thereis provided a CO₂ refrigeration system for an ice-playing surface,comprising: a CO₂ refrigerant circuit comprising a condensationreservoir accumulating a portion of the CO₂ refrigerant in a liquidstate, and an evaporation stage receiving the CO₂ refrigerant from thecondensation reservoir, the evaporation stage having a circuit of pipesarranged under the ice-playing surface, whereby the CO₂ refrigerantcirculating in the circuit of pipes of the evaporation stage absorbsheat from the ice-playing surface; an independent refrigerant circuit inheat-exchange relation with the CO₂ refrigerant of the CO₂ refrigerantcircuit, the independent refrigerant circuit comprising a compressionstage with at least one magnetically-operated compressor to compress asecondary refrigerant, a condensation stage in which the secondaryrefrigerant releases heat, and an evaporation stage in which thesecondary refrigerant is in heat exchange relation with the CO₂refrigerant circuit by a heat exchanger to absorb heat therefrom.

Further in accordance with the second embodiment, the system furthercomprises a line extending from a top of the condensation reservoir tothe heat exchanger, such that gaseous CO₂ refrigerant in thecondensation reservoir is directed to the independent refrigerantcircuit.

Still further in accordance with the present disclosure, there isprovided a CO₂ refrigeration system for an ice-playing surface,comprising: a compression portion comprising: a compression stagecomprising at least one compressor in which CO₂ refrigerant iscompressed to a transcritical state; a gas cooling stage in which theCO₂ refrigerant compressed to the transcritical state releases heat byheat exchange with a gas; pressure-regulating means downstream of thegas cooling stage to control a pressure of the CO₂ refrigerant in thecompression portion of the CO₂ refrigeration system; and an oil circuitin the CO₂ refrigeration system, the oil circuit collecting oildownstream of the at least one compressor in the compression stage, theoil circuit directing the oil upstream of the at least one compressorfor the CO₂ refrigerant fed to the compressor to have an oil content.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a CO₂ refrigeration system in accordancewith an embodiment of the present application;

FIG. 2 is a block diagram of the CO₂ refrigeration system of FIG. 1,with an example of operating pressures for a cold climate application;

FIG. 3 is a block diagram of the CO₂ refrigeration system of FIG. 1,with an example of operating pressures for a warm climate application;and

FIG. 4 is a schematic view of a line used with the CO₂ refrigerationsystem, in accordance with another embodiment of the presentapplication.

FIG. 5 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment,

FIG. 6 is a schematic view of a line configuration for a refrigerationunit, in accordance with yet another embodiment of the presentapplication;

FIG. 7 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment, with dedicated compression for defrost;

FIG. 8 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment, e.g., for a skating rink application;

FIG. 9 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment, with a supra-compression providing defrost;

FIG. 10 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment, with cascaded compression;

FIG. 11 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment, with suction accumulation upstream of asupra-compression stage;

FIG. 12 is a block diagram of a CO₂ refrigeration system in accordancewith another embodiment, with a heat-exchanger for defrost refrigerant;and

FIG. 13 is a schematic view of a desiccant system in accordance withanother embodiment of the present application.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a CO₂ refrigeration system in accordance with anembodiment is illustrated at 1. The CO₂ refrigeration system 1 has a CO₂refrigeration circuit comprising a CO₂ compression stage 10. CO₂refrigerant is compressed in the compression stage 10, and issubsequently directed via line 11 to a condensation reservoir 12, or toa heat-reclaim stage 13.

The condensation reservoir 12 accumulates CO₂ refrigerant in a liquidand gaseous state, and is in a heat-exchange relation with acondensation circuit that absorbs heat from the CO₂ refrigerant. Thecondensation circuit is described in further detail hereinafter.Moreover, a transcritical circuit and a defrost circuit may supply CO₂refrigerant to the condensation reservoir 12, as is described in furtherdetail hereinafter.

The heat-reclaim stage 13 is provided to absorb heat from the CO₂refrigerant exiting from the compression stage 10. The heat-reclaimstage 13 may take various forms, such as that of a heat exchanger bywhich the CO₂ refrigerant is in heat exchange with an alcohol-basedrefrigerant circulating in a closed loop. As another example, theheat-reclaim stage 13 features coils by which the CO₂ refrigerantreleases heat to a water tank.

Line 14 directs CO₂ refrigerant from the condensation reservoir 12 to anevaporation stage via expansion valves 15. As is shown in FIG. 1, theCO₂ refrigerant is supplied in a liquid state by the condensationreservoir 12 into line 14. The expansion valves 15 control the pressureof the CO₂ refrigerant, which is then fed to either low-temperatureevaporation stage 16 or medium-temperature evaporation stage 17. Boththe evaporation stages 16 and 17 feature evaporators associated withrefrigerated enclosures, such as closed or opened refrigerators,freezers or the like. It is pointed out that the expansion valves 15 maybe part of a refrigeration pack in the mechanical room, as opposed tobeing at the refrigeration cabinets. As a result, flexible lines (e.g.,plastic non-rigid lines) could extend from the expansion valves 15 todiffuser upstream of the coils of the evaporation stages 16 and 17. Thevalves 15 may be at the refrigeration cabinets, at the refrigerationpack in a mechanical room, or any other suitable location.

CO₂ refrigerant exiting the low-temperature evaporation stage 16 isdirected to the CO₂ compression stage 10 via line 18 to complete arefrigeration cycle. A heat exchanger 19 is provided in the line 18, andensures that the CO₂ refrigerant is fed to the compression stage 10 in agaseous state. Other components, such as a liquid accumulator, may beused as an alternative to the heat exchanger 19. As describedhereinafter, the heat exchanger 19 may be associated with a condensationcircuit.

CO₂ refrigerant exiting the medium-temperature evaporation stage 17 isdirected to the transcritical circuit as is described hereinafter.

A condensation circuit has a heat exchanger 20. The heat exchanger 20 isin fluid communication with the condensation reservoir 12, so as toreceive CO₂ refrigerant in a gaseous state. The condensation circuit isclosed and comprises a condensation refrigerant that also circulates inthe heat exchanger 20 so as to absorb heat from the CO₂ refrigerant.

In the condensation circuit, the condensation refrigerant circulatesbetween the heat exchanger 20 in which the condensation refrigerantabsorbs heat, a compression stage 21 in which the condensationrefrigerant is compressed, and a condensation stage 22 in which thecondensation refrigerant releases heat. The compression stage 21 may useTurbocor™ compressors. In an example, the condensation stage 22 featuresheat reclaiming (e.g., using a heat exchanger with a heat-transferfluid) in parallel or in series with other components of thecondensation stage 22, so as to reclaim heat from the CO₂ refrigerant.Although not shown, the condensation circuit may be used in conjunctionwith the heat exchanger 19, so as to absorb heat from the CO₂refrigerant being directed to the compression stage 10. In this case,the condensation refrigerant is in a heat-exchange relation with the CO₂refrigerant.

It is pointed out that the condensation circuit may be used with morethan one CO₂ refrigeration circuit. In such a case, the condensationcircuit features a plurality of heat exchangers 20, for instance withone for each of the CO₂ refrigeration circuits.

Examples of the condensation refrigerant are refrigerants such as R-404and R-507, amongst numerous examples. It is observed that thecondensation circuit may be confined to its own casing as illustrated inFIG. 1. Moreover, considering that the condensation circuit ispreferably limited to absorbing heat from stages on a refrigeration pack(e.g., condensation reservoir 12, suction header in line 18), thecondensation circuit does not contain a large volume of refrigerant whencompared to the CO₂ refrigeration circuit, of a secondary refrigerantcircuit defined hereinafter.

The transcritical circuit (i.e., supra-compression circuit) is providedto compress the CO₂ refrigerant exiting from the medium-temperatureevaporation stage 17 to a transcritical state, for heating purposes, orsupra-compressed state. In both compression states, the CO₂ refrigerantis pressurized in view of maintaining the condensation reservoir 12 at ahigh enough pressure to allow vaporized CO₂ refrigerant to be circulatedin the evaporation stages 16 and 17, as opposed to liquid CO₂refrigerant.

A line 30 relates the medium-temperature evaporation stage 17 to a heatexchanger 31 and subsequently to a supra-compression stage 32. The heatexchanger 31 is provided to vaporize the CO₂ refrigerant fed to thetranscritical compression stage 32. The supra-compression stage 32features one or more compressors (e.g., Bock™, Dorin™), that compressthe CO₂ refrigerant to a supra-compressed or transcritical state.

In the transcritical state, the CO₂ refrigerant is used to heat asecondary refrigerant via heat-reclaim exchanger 34. In the heat-reclaimexchanger 34, the CO₂ refrigerant is in a heat-exchange relation withthe secondary refrigerant circulating in the secondary refrigerantcircuit 35. The secondary refrigerant is preferably anenvironmentally-sound refrigerant, such as water or glycol, that is usedas a heat-transfer fluid. Because of the transcritical state of the CO₂refrigerant, the secondary refrigerant circulating in the circuit 35reaches a high temperature. Accordingly, due to the high temperature ofthe secondary refrigerant, lines of smaller diameter may be used for thesecondary refrigerant circuit 35. It is pointed out that the secondaryrefrigerant circuit 35 is the largest of the circuits of therefrigeration system 1 in terms of quantity of refrigerant. Therefore,the compression of the CO₂ refrigerant into a transcritical state by thetranscritical circuit allows the lines of the secondary refrigerantcircuit 35 to be reduced in terms of diameter.

A gas cooling stage 36 is provided in the transcritical circuit. The gascooling stage 36 absorbs excess heat from the CO₂ refrigerant in thetranscritical state, in view of re-injecting the CO₂ refrigerant in thecondensation reservoir 12. Although it is illustrated in a parallelrelation with the heat-reclaim exchanger 34, the gas cooling stage 36may be in series therewith, or in any other suitable arrangement.Although not shown, appropriate valves are provided so as to control theamount of CO₂ refrigerant directed to the gas cooling stage 36, in viewof the heat demand from the heat-reclaim exchanger 34.

In warmer climates in which the demand for heat is smaller, the CO₂refrigerant is compressed to a supra-compressed state, namely at a highenough pressure to allow the expansion of the CO₂ refrigerant at theexit of the condensation reservoir 12, so as to reduce the amount of CO₂refrigerant circulating in the refrigeration circuit. A by-pass line isprovided to illustrate that the heat-reclaim exchanger 24 and the gascooling stage 36 are optional for warmer climates.

The gas cooling stage 36 may feature a fan blowing a gas refrigerant oncoils. The speed of the fan may be controlled as a function of the heatdemand of the heat reclaim exchanger 34. For an increased speed of thefan, there results an increase in the temperature differential atopposite ends of the gas cooling stage 36.

Lines 37 and 38 return the CO₂ refrigerant to the condensation reservoir12, and thus to the refrigeration circuit. The line 37 feeds the heatexchanger 31 such that the CO₂ refrigerant exiting the stages 34 and 36release heat to the CO₂ refrigerant fed to the supra-compression stage32. Accordingly, the CO₂ refrigerant fed to the supra-compression stage32 is in a gaseous state.

In the case of transcritical compression, a CO₂ transcriticalpressure-regulating valve 39 is provided to maintain appropriatepressures at the stages 34 and 36, and in the condensation reservoir 12.The CO₂ transcritical pressure-regulating valve 39 is for instance aDanfoss™ valve. Any other suitable pressure-control device may be usedas an alternative to the valve 39, such as any type of valve or loop.

The condensation circuit and the supra-compression circuit allow thecondensation reservoir 12 to store refrigerant at a relatively mediumpressure. Accordingly, no pump may be required to induce the flow ofrefrigerant from the condensation reservoir 12 to the evaporation stages16 and 17. As CO₂ refrigerant is vaporized downstream of the expansionvalves 15, the amount of CO₂ refrigerant in the refrigeration circuit isreduced, especially if the expansion valves 15 are in the refrigerationpack.

It is considered to operate the supra-compression circuit (i.e., supracompression 32) with higher operating pressure. CO₂ refrigerant has asuitable efficiency at a higher pressure. More specifically, more heatcan be extracted when the pressure is higher.

The refrigeration system 1 may be provided with a refrigerant defrostsystem. In FIG. 1, a portion of the CO₂ refrigerant exiting from thecompression stage 10 is directed to the evaporation stages 16 and 17.Although not shown, appropriate valves and pressure-reducing devices areprovided to stop the flow of cooling CO₂ refrigerant in the evaporatorsin view of the defrost. The defrost CO₂ refrigerant releases heat todefrost any frost build-up on the evaporators of the evaporation stages16 and/or 17.

Although not shown, other compression configurations may be used tosupply defrost refrigerant to the evaporators, such as dedicatedcompressors, cascaded compressors of the like.

Line 41 directs the defrost CO₂ refrigerant having released heat to thedefrost reservoir 42. The defrost reservoir 42 accumulates the defrostCO₂ refrigerant, and features a line 43 with a control valve (e.g.,exhaust valve, check valve), so as to allow gaseous CO₂ refrigerant tobe sucked back into the CO₂ refrigeration circuit by the CO₂ compressionstage 10. The defrost reservoir 42 is an option, as the evaporationstages 16 and 17 may direct the refrigerant to other reservoirs oraccumulators of any other refrigeration system presenter herein.

A flush of the defrost reservoir 42 may be performed periodically, so asto empty the defrost reservoir 42. Accordingly, lines 44 and 45, withappropriate valves, allow the flush of the liquid CO₂ refrigerant fromthe defrost reservoir 42 to the condensation reservoir 12.

A pressure-reducing valve 46 may be provided in the line 40 or line 11to regulate a pressure of the defrost CO₂ refrigerant fed to theevaporation stage 16 and/or 17 for defrost. Valves, such as check valve47, are as relief valves for the evaporation stages 16 and 17. Forinstance, in case of a power shortage, the CO₂ refrigerant in theevaporators may increase in pressure. Accordingly, the check valves 47open at a threshold pressure to allow the CO₂ refrigerant to reach thedefrost reservoir 42.

Considering that the compressors of the CO₂ compression stage 10 or ofthe compression stage 21 are low-consumption compressors, thesecompressors may be operated during a power outage to maintain suitablerefrigerating conditions in the evaporation stages 16 and 17. Thecompressors of the compression stage 21 may also be Turbocor™compressors.

As an alternative to the defrost circuit, the evaporators of theevaporation stages 16 and 17 may be equipped with electric coils for theelectric defrost of the evaporators.

In an embodiment, the casing enclosing the condensation circuit may alsocomprise an air-conditioning unit 50. Accordingly, the roof-topequipment associated with the refrigeration system 1 is provided in asingle casing, thereby facilitating the installation thereof. Moreover,it is considered to unite as many components of the refrigeration system1 in a single refrigeration pack. For instance, the compressors of theCO₂ compression stage 10, the condensation reservoir 12, the expansionvalves 15, and optionally the compressors from the supra-compressionstage 32, as well as the defrost reservoir 42 may all be provided in asame pack, with most of the lines joining these components. Theinstallation is therefore simplified by such a configuration.

In order to illustrate the operating pressures of the CO₂ refrigerationsystem 1 in cold and warm climates, FIGS. 2 and 3 are respectivelyprovided with pressure values. It is pointed out that all values arejust an illustration, whereby pressure values could be higher or lower.FIG. 2 shows operating pressures for the CO₂ refrigeration system 1 asused in cold climates (e.g., winter conditions in colder regions), witha demand for heat by the secondary refrigerant circuit 35. FIG. 3 showsoperating pressures for the CO₂ refrigeration system as used in warmclimates (e.g., summer conditions, warmer regions).

Although not fully illustrated, numerous valves are provided to controlthe operation of the CO₂ refrigeration system 1 as described above.Moreover, a controller A ensures that the various stages of therefrigeration system 1 operate as described, for instance by having aplurality of sensors places throughout the refrigeration system 1.

Referring to FIG. 3, there is illustrated a safety valve circuit 55 soas to ensure that the refrigerant pressure in the coils of theevaporation stages 16 and 17 does not exceed a given maximum value(e.g., 410 Psi), which may result in damages to the coils. The safetyvalve circuits 55 extends from the evaporation stages 16 and 17 (e.g.,lines at the exit of the coils) to the defrost reservoir 42. A safetyvalve 56 is provided in the circuit, and operates by monitoring thepressure in the coils and opening as a result of the pressure reachingthe maximum value. The defrost reservoir 42 then absorbs the excesspressure by receiving the refrigerant. The defrost reservoir 42subsequently discharges the refrigerant using the lines describedpreviously.

Referring to FIG. 4, a line that may be used in the CO₂ refrigerationsystem 1 is illustrated at 60. The line 60 is a flexible hose adapted tosupport the relatively high pressures associated with CO₂ refrigerant.One suitable example of flexible hose is the “Transfer Oil” hydraulichose by Gomax™. The hose 60 is rodded into a conduit of sleeves 61 of aninsulating material, such as urethane, positioned end to end to coverthe length of hose 60. A plurality of hoses 60 may be used with a singlesleeve 61, provided the inner diameter of the sleeve 61 is large enoughto receive the hoses 60. Therefore, by the use of flexible hoses, theinstallation of the lines is simplified. Previous lines required weldingoperation to join tubes of metallic material.

Referring to FIG. 5, an alternative embodiment of the CO₂ refrigerationsystem 1 of FIGS. 1-3 is illustrated at 70. The CO₂ refrigerationsystems 1 and 70 have numerous common stages and lines, whereby likeelements will bear like reference numerals. One difference between theCO₂ refrigeration systems 1 and 70 is the absence of a condensationcircuit such as the one having the heat exchanger 20 in FIGS. 1-3.Rather, the CO₂ refrigerant in the condensation reservoir 12 is cooledby the transcritical circuit (i.e., supra-compression circuit) featuringthe heat exchanger 31.

Therefore, a line 71 extends from the condensation reservoir 12 anddirects CO₂ refrigerant to the hot side of the heat exchanger 31, whichheat exchanger 31 is optional and is used to vaporize the CO₂refrigerant if necessary. The line 71 may be collecting gas CO₂refrigerant at a top of the condensation reservoir 12 to direct the CO₂refrigerant to the heat exchanger 31. A pressure-reducing valve 72 isprovided in line 71 to ensure that the CO₂ refrigerant reaches the heatexchanger 31 at a suitable pressure. The CO₂ refrigerant goes throughthe supra-compression circuit in the manner described previously, so asto lose heat, and return to the condensation reservoir 12 primarily in aliquid state.

It is pointed out that the configuration of the CO₂ refrigeration system70 of FIG. 5 is such that a single refrigerant, namely CO₂ refrigerant,is used therein.

Referring to FIG. 6, an alternative line configuration is shown at 80,which line configuration is typically used to supply refrigerant tolarge refrigeration units (e.g., in freezer rooms). Line 81, typically alarge diameter line, diverges into a plurality of smaller lines, from anexpansion valve 82. Each smaller line may have a valve 83, and eachfeeds an own smaller refrigeration unit 84. As a result, some of theunits 84 may be turned off, so as to meet more precisely the cool demandof an enclosure.

Referring to FIG. 7, yet another embodiment of a CO₂ refrigerationsystem is illustrated at 90. The CO₂ refrigeration systems 1 and 90 havenumerous common stages and lines, whereby like elements will bear likereference numerals. One difference between the CO₂ refrigeration systems1 and 90 is the presence of at least one dedicated compressor 10′ tocompress defrost refrigerant. The discharge of the dedicated compressor10′ goes at least partially to the defrost circuit, whereas thedischarge of the other compressors 10 is directed to the refrigerationcircuit. A line and valve (not shown) may be used to direct some excessrefrigerant from the dedicated compressor 10′ to the refrigerationcircuit. The CO₂ dedicated compressor 10′ may also be used to flush thedefrost reservoir 42.

As an alternative, defrost could be made by directing refrigerant fromthe supra-compression circuit, into the defrost circuit, using anappropriate pressure-reducing valve.

Referring to FIG. 8, yet another embodiment of a CO₂ refrigerationsystem is illustrated at 100. The CO₂ refrigeration systems 70 (FIG. 5)and 90 have numerous common stages and lines, whereby like elements willbear like reference numerals. The CO₂ refrigeration system 100 is wellsuited for applications requiring low-temperature cooling, such asice-skating rinks and industrial freezer applications.

The CO₂ refrigeration system 100 may be configured to operate withoutthe CO₂ compression stages, due to the heat removal capacity of thesupra-compression circuit. In such a configuration, a pump may circulatethe refrigerant in the refrigeration circuit, from the condensationreservoir 12 to the low-temperature evaporation 16. In the ice-skatingrink applications, the various heat absorbing components (e.g., the heatreclaim stage 13, the heat reclaim exchanger 34) may be used to meltzamboni residue in an ice dump. It is preferred not to use thesupra-compression circuit when the CO₂ refrigeration system 100 isoperated in warmer countries. The CO₂ refrigeration system 100 is moreefficient with CO₂ compression in such climates.

Considering the nature of the refrigerant, plastic tubing or non-rigidlines may be used as an alternative to the rigid metallic linespreviously used, between the mechanical room and the stages of thesystems, such as the condensation stage 12 and the evaporation stages 16and 17. One known type of pipes that can be used is Halcor Cusmartpipes, and features a non-rigid copper core with a plastic insulationsleeve about the core. Such configurations are cost-efficient in that noweld joints are required to interconnect pipes, as is the case for rigidmetallic lines. Gutters, for instance having a trapezoid cross-section,may be used as a guide for lines.

Referring to FIG. 9, yet another embodiment of a CO₂ refrigerationsystem is illustrated at 110. The CO₂ refrigeration systems 1 and 110have numerous common stages and lines, whereby like elements will bearlike reference numerals. One difference between the CO₂ refrigerationsystems 1 and 110 is line 111 directing CO₂ refrigerant from thesupra-compression stage 32 to the evaporator stages 16 and 17 fordefrost. Accordingly, the CO₂ refrigerant fed to the evaporation stage16/17 is at a relatively high pressure—valve 114 may be provided tolower the pressure of the CO₂ refrigerant to an appropriate level (e.g.,500 Psi). The defrost refrigerant is then directed to the defrostreservoir 42. A valve 112 is provided to control the amount of defrostrefrigerant from the reservoir 42 reintegrating the refrigeration cycle.Moreover, in order to maintain a suitable compression ratio in view ofthe operating pressure of the condensation reservoir 12, apressure-reducing valve 113 is provided in the line 11, so as to reducethe pressure of the CO₂ refrigerant feeding the condensation reservoir12.

Moreover, the refrigeration system 110 has a line 115 (with appropriatevalves) selectively directing refrigerant from the supra-compressionstage 32 to the defrost reservoir 42, to flush the reservoir 42 whenrequired. It is pointed out that the heat exchangers 19 and 31 areoptional, as is the condensation circuit featuring the compression stage21.

Referring to FIG. 10, yet another embodiment of a CO₂ refrigerationsystem is illustrated at 120. The CO₂ refrigeration systems 70 and 120have numerous common stages and lines, whereby like elements will bearlike reference numerals. The CO₂ refrigeration system 120 has a cascadedarrangement for the two stages of CO₂ compression, namely compressionstage 10 and supra-compression stage 32. More specifically, therefrigerant discharge from the compression stage 10 is fed to a suctionaccumulator 121, and CO₂ refrigerant in a gas state is sucked from a topof the accumulator 121 by the supra-compression stage 32.

The suction accumulator 121 also receives CO₂ refrigerant from theevaporation stage 17, optionally via heat exchanger 31. Gas CO₂refrigerant from the condensation reservoir 12 may also be directed tothe suction accumulator 121. The liquid CO₂ refrigerant from the suctionaccumulator 121 may be directed to the compression stage 10.

In order to maintain suitable conditions for the refrigerant at theinlet of the compression stage, a first suction accumulator 122 isprovided downstream of the compression stage 10, which suctionaccumulator 122 receives CO₂ refrigerant from the suction accumulator121 through a line (e.g., capillary) having a heat exchanger 123 forheat exchange with a discharge of the supracompression stage 32, or witha discharge of the compression stage 10. Moreover, liquid refrigerantfrom the suction accumulator 122 may be heated by line 124, in heatexchange with the discharge of the compression stage 10 or withsupracompression stage 32, or simply by using an electric heater. Theline 124 may then direct the vaporized refrigerant to the suction of thecompression stage 10. In an embodiment, the line 124 collects liquid CO₂refrigerant and oil at a bottom of the suction accumulator 122.Accordingly, the vaporized refrigerant has an oil content when fed tothe compressors of the compression stage 10. The oil is then recuperatedfor instance in the suction accumulator 121. A similar loop may beperformed to feed a mixture of CO₂ refrigerant and oil to thesupra-compression stage 32.

In the embodiment in which the line 124 directs vaporized refrigerant tothe suction of the compression stage 10, a valve 125 is provided in thatcase to maintain a pressure differential between the suction accumulator122 and the suction of the compression stage 10, to allow the flow ofrefrigerant from line 124 into CO₂ compression stage 10. It isconsidered to use other components than suction accumulator 121, suctionaccumulator 122, line 124 and heat exchanger 123 to vaporize therefrigerant, such as a heating element, an air conditioning system, aheat exchanger and the like. It is also considered that CO₂ refrigerantleaving suction accumulator 121 and suction accumulator 122 be directedelsewhere in the CO₂ refrigeration system.

The cascaded compressor configuration of FIG. 10 is well suited topreserve the oil in the compression stage 10. More specifically, oilaccumulating in the suction accumulator 121 is returned to the suctionaccumulator 122 via the line of heat-exchanger 123. The oil may then besucked with refrigerant by the compression stage 10. Accordingly, theoil cycles between stages 10, 121 and 122. A similar cycle may be usedfor feeding an oil and refrigerant mixture to the supra-compressionstage 32.

The defrost of the evaporation stages 16 and 17 may be performed at lowpressure so as to avoid damaging the evaporator coils. Accordingly, therefrigeration cycle 120 may be retrofitted to existing evaporator coils,considering the relatively low defrost pressures. The defrost CO₂refrigerant may be fed by the compression stage 10, or by the supracompression stage 32, with valve 46 controlling the pressure.

In order to protect the evaporator coils from high defrost pressures, aset of lines 126 extends from the evaporator coils to any reservoir oraccumulator of the refrigeration system 120. For instance, the lines 126are connected to one of the accumulators 121 and 122 while beingseparated by a valve 127. The valve 127 opens if the pressure in theevaporator coils is above a given threshold. Accordingly, if the defrostpressure in the evaporator coils is too high, the defrost CO₂refrigerant is discharged to one of the accumulators 121 and 122,whereby the CO₂ refrigerant stays in the refrigeration system 120. Asanother safety measure, a pressure-relief valve system 128 is providedon the appropriate accumulators, such as 122 as shown but alternativelyon the accumulator 121 or on the condensation reservoir 12.

For instance, the method for relieving CO₂ refrigerant pressure fromevaporators during a defrost cycle comprises providing a pressure-reliefvalve for each evaporator line, the pressure relief-valve opening at apressure threshold. CO₂ refrigerant is then fed to evaporators in theevaporator line to defrost the evaporator. The evaporators are exhaustedfrom the CO₂ refrigerant with the pressure-relief valve when the CO₂refrigerant pressure is above the pressure threshold; and directing theexhausted CO₂ refrigerant to an accumulator in a refrigeration cycle.

In specific conditions, it may be required to cool the CO₂ refrigerantfed to the evaporation stages 16 and/or 17 during the refrigerationcycle. Accordingly, a heat-exchanger system 129, for instance with anexpansion valve, may direct refrigerant from the line 71 and feed sameto the heat-exchanger system 129, to cool the CO₂ refrigerant fed to theevaporation stages 16 and/or 17.

The valve 39 is controlled (e.g., modulated) to maximize the heatreclaim via the heat reclaim exchanger 34. When the heat demand is high(e.g., during Winter in colder climates), the valve 39 may maintain ahigh refrigerant pressure downstream of the compression stage 32, toensure the heat reclaim exchanger 34 extracts as much heat as possiblefrom the CO₂ refrigerant. The amount of refrigerant sent to the gascooling stage 36 is controlled simultaneously.

Referring to FIG. 11, yet another embodiment of a CO₂ refrigerationsystem is illustrated at 130. The CO₂ refrigeration systems 1 and 130have numerous common stages and lines, whereby like elements will bearlike reference numerals. The CO₂ refrigeration system 130 isparticularly well suited for hot climate applications. In the CO₂refrigeration system 130, the discharge of the compression stage 10 isdirected to the heat exchanger 20 prior to reaching the condensationreservoir 12, for relatively low pressure condensation. Alternatively,the refrigerant exiting the heat exchanger 20 may be directed to thesuction accumulator 133, thereby bypassing the condensation reservoir12. A gaseous portion of the CO₂ refrigerant in the condensationreservoir 12 is directed via line 131 and pressure-reducing valve 132into the heat exchanger 31 to reach the suction accumulator 133. The CO₂refrigerant passing through the heat exchanger 31 absorbs heat from theCO₂ refrigerant exiting the supra-compression circuit via line 134. Aline 135 relates a top of the suction accumulator 133 to thesupra-compression stage 32, to feed gaseous CO₂ refrigerant to thecompressors. Liquid CO₂ refrigerant may be directed to another suctionaccumulator 136, at the suction of the compression stage 10, in similarfashion to the CO₂ refrigeration system 120 of FIG. 10 (with appropriateheat exchange with the discharge of stage 10 if necessary). Thesupra-compression circuit is typically used to reclaim heat, while theevaporation stages 16 and 17 are part of a HVAC unit, amongst otherpossibilities.

Referring to FIG. 12, yet another embodiment of a CO₂ refrigerationsystem is illustrated at 140. The CO₂ refrigeration systems 1 and 140have numerous common stages and lines, whereby like elements will bearlike reference numerals. The CO₂ refrigeration system 140 has a heatexchanger 141 collecting defrost CO₂ refrigerant at the outlet of theevaporators 16/17, to vaporize the defrost CO₂ refrigerant and returnsame into the refrigeration cycle, namely to feed the suction of thecompression stage 10 via line 142 or the supra-compression stage 32 vialine 143. The heat exchanger 141 allows heat exchange between thedefrost CO₂ refrigerant and the CO₂ refrigerant exiting thesupra-compression stage 32 via lines 144, and may also be any other heatsource (e.g. electric heater, heat reclaim, air-conditioning unit, orthe like).

An air-conditioning unit 145 may be in fluid communication with thedefrost reservoir 42 so as to use the defrost CO₂ refrigerantaccumulated therein for air-conditioning purposes. The discharge of theair-conditioning unit 145 may be returned to the suction of thesupra-compression stage 32, amongst other possibilities. In the variousrefrigerant systems described above, it is pointed out that the defrostrefrigerant may be fed to the evaporators of stages 16 and 17 fromeither direction (as opposed to being fed in a direction opposed to thatof refrigerant in the refrigeration cycle). Moreover, it is consideredto provide the valves controlling the flow of defrost refrigerant to theevaporators 16 and 17 in the refrigeration pack, and have a plurality oflines for each single valve.

Referring to FIG. 13, a desiccant system is generally shown at 150. Thedesiccant system 150 may be used with any of the refrigeration systemsdescribed above, or with other refrigeration systems, to dry air beingentered into a building for ventilating or refrigerating purposes. Thedesiccant system 150 is a closed circuit in which circulates a desiccantfluid.

The system 150 has a dryer 151, upon which exterior air flows whenentering the building. The dryer 151 is a structural device upon whichthe desiccant fluid is sprayed. For instance, the dryer 151 may providea honeycomb body. The desiccant fluid sprayed on the dryer 151 is in asuitable cooled state to absorb humidity from the warm exterior airentering the building. The desiccant fluid reaches a substantiallyliquid state after the absorption of humidity, and drips into pan 152(or any oter collector).

By way of a line and pump, the desiccant fluid passes through a heatingexchanger 153 to be heated. Although not shown, the heating exchanger153 may be connected to one of the above-referred refrigerationcircuits, so as to provide the necessary energy to heat the desiccantfluid. Alternatively, the heating exchanger 153 may have an electriccoil or the like.

The desiccant fluid, in a heated state, is then sprayed onto ahumidifier 154. The humidifier 154 is similar to the dryer 151 inconstruction, but releases water to the exterior air. The desiccantfluid is heated as a function of the exterior temperature, for thedesiccant fluid to release the previously-absorbed water to the air. Theliquid desiccant is then collected in another pan 155 (or the like).

By way of a line and pump, the desiccant fluid passes through a coolingexchanger 156 to be cooled. Although not shown, the cooling exchanger156 may be connected to one of the above-referred refrigerationcircuits, so as to provide the necessary energy to cool the desiccantfluid. The desiccant fluid is cooled as a function of the exteriortemperature, for the desiccant to absorb water from the outdoor airentering the building. Once it is cooled, the desiccant fluid isdirected to the dryer 151.

1. A method for operating a CO₂ refrigeration system for an ice-playingsurface, comprising: operating a refrigeration cycle by sequentiallycompressing CO₂ refrigerant, releasing heat from the CO₂ refrigerant ina gas cooling stage after the compressing, absorbing heat from at leastone ice-playing surface after the releasing, and directing the CO₂refrigerant having absorbed heat to the compressing; and for a heatdemand of a plurality of heat-reclaim units, causing the pressure of theCO₂ refrigerant to reach a transcritical level as a function of saidheat demand for the plurality of heat-reclaim units to absorb heat fromthe CO₂ refrigerant in the gas cooling stage.
 2. The method according toclaim 1, further including causing the pressure of the CO₂ refrigerantto return to a subcritical level from said transcritical level as afunction of said heat demand.
 3. The method according to claim 1,wherein causing the pressure of the CO₂ refrigerant to reach atranscritical level includes controlling a pressure-regulating devicedownstream of the gas cooling stage.
 4. The method according to claim 1,further including accumulating CO₂ refrigerant in a liquid state in areservoir prior to said absorbing heat.
 5. The method according to claim1, wherein absorbing heat from at least one ice-playing surface includescirculating CO₂ refrigerant in a circuit of pipes to absorb heat fromthe at least one ice-playing surface.
 6. The method according to claim5, wherein circulating CO₂ refrigerant in a circuit of pipes includesvaporizing the CO₂ refrigerant with at least one expansion valve.
 7. Themethod according to claim 5, wherein circulating CO₂ refrigerant in acircuit of pipes includes pumping the CO₂ refrigerant in the liquidstate into the circuit of pipes.
 8. The method according to claim 1,wherein at least one of the plurality of heat-reclaim units absorbs heatfrom the CO₂ refrigerant in the gas cooling stage by heat exchange witha secondary refrigerant.
 9. The method according to claim 8, wherein thesecondary refrigerant heats water in at least one water tank.
 10. Themethod according to claim 1, wherein the plurality of heat-reclaim unitsabsorbs heat from the CO₂ refrigerant in the gas cooling stage inseries.
 11. The method according to claim 1, wherein the plurality ofheat-reclaim units absorbs heat from the CO₂ refrigerant in the gascooling stage in parallel.
 12. The method according to claim 1, whereinat least one of the plurality of heat-reclaim units absorbs heat fromthe CO₂ refrigerant in the gas cooling stage by blowing air on a coil inwhich circulates the CO₂ refrigerant.
 13. The method according to claim1, further including collecting oil downstream of said compressing, anddirecting the oil upstream of said compressing for the CO₂ refrigerantin said compressing to have an oil content.
 14. The method according toclaim 13, wherein collecting oil includes collecting oil from a bottomof a reservoir.
 15. The method according to claim 3, wherein controllingthe pressure-regulating device downstream of the gas cooling stageincludes modulating a valve to maximize the heat reclaim as a functionof the heat demand of the plurality of heat-reclaim units.
 16. Themethod according to claim 1, wherein causing the pressure of the CO₂refrigerant to reach a transcritical level as a function of said heatdemand includes causing the pressure of the CO₂ refrigerant to reach apressure of at least 1400 Psi as a function of the heat demand during awinter month period.
 17. The method according to claim 16, whereincausing the pressure of the CO₂ refrigerant to reach a transcriticallevel as a function of said heat demand includes causing the pressure ofthe CO₂ refrigerant to reach a pressure including 550 Psi as a functionof the heat demand during a summer month period, wherein an outdoortemperature is warmer in the summer month period than in the wintermonth period.